Pan and Zoom (opacity, to see backround)

Welcome,

I would like merege some movies, te first one i want move to the right and combine it together.

I'm trying Pan and Zoom but always when i move first clip, i cant see what's under but i see black background.

I attach screenshot.

You can see, i add 2 colors and move first using pan.
But i got black background. It should be blue (second clip whats under first).

Any idea ?

Regards

Make sure you apply the composite transition correctly.